Point of Care Tests have become increasingly common over the past several years. These tests are simple to perform, require little or no extra equipment, and typically produce results in a relatively short period of time compared to traditional laboratory tests. There are primarily two technological platforms available in the Point of Care test market: lateral flow and flow-through, each of which can be used for many applications.
While both lateral flow and flow-through test devices utilize the same biological principles, namely detection of target analytes such as antibodies or antigens in a bodily fluid, they differ in their methods for detecting antibody-antigen complexes.
For example, Eisinger et al., U.S. Pat. No. 4,943,522, describes a lateral flow diagnostic device in which the test sample is applied to one end of the device and then transferred laterally across a membrane to be visualized in one or more indicator zones.
A common problem with most lateral flow devices is that the amount of time required to transfer the test sample laterally from the sample application zone to the indicator zones may not be ideal for certain time sensitive applications, such as emergency departments, labour and delivery settings and needle stick injuries.
Accordingly, flow-through devices offer advantages over lateral flow devices in that they are often more compact and can provide more rapid results. Examples of such flow-through devices can be found in Brown et al., U.S. Pat. No. 5,160,701 and Chan, U.S. Pat. No. 7,531,362.
Brown et al., USP '701 describe a flow-through device in which the fluid test sample is applied to a reaction matrix containing a capture reagent bound to the matrix that is capable of binding to a target analyte in the test sample. The remaining portion of the test sample flows through the reaction matrix into an absorbent pad. After several rounds of washing, the presence or absence of the target analyte in the fluid test sample is visually determined following the manual addition of a liquid indicator reagent. The Brown et al., device requires the manual addition of several buffers and reagents in order to achieve a result. These manual steps not only increase the amount of time required to complete an assay, but also increase the potential for error in the assay. In addition, some of reagents required for use with the Brown et al., device require refrigeration or have to be prepared immediately prior to use in the assay, thus limiting the environments in which the device can be used.
Chan, USP '362, provides a flow-through device that eliminates several of the washing steps required by Brown et al., thus decreasing the overall time required to successfully complete an assay. Furthermore, Chan provides a post-filter unit containing a dried indicator reagent that is applied to the test device after the test sample has permeated through the reaction matrix. A buffer is applied to the post-filter unit to resolubilize the indicator reagent. The resolubilized indicator reagent is then able to interact with the two-membered complex formed in the reaction zone between the target analyte and the capture reagent. By providing the indicator reagent in a dried format in a post-filter unit, the assay requires only a single buffer, fewer washing steps, and can be stored at room temperature.
Although the Chan device efficiently provides results in a timely manner, it would be desirable to have a rapid diagnostic device that improves the efficiency of the Chan device by further reducing the required number of manual additions of reagents and buffers than the traditional downward or vertical flow through devices.